Malware such as viruses, worms and Trojans, have become the principle threat to the normal functioning of computers and to the information stored in them. The scope and range of malicious software is constantly expanding, presenting an ever-growing security challenge. Malicious programs are also making use of new methods to penetrate computer systems, concealing their activities and bypassing detection by security software. No conventional malware detection method can now provide complete protection when used as a stand-alone tool.